Why Are Prion Diseases on the Rise?

This transcript has been edited for clarity.

In 1986, in Britain, cattle started dying.

The condition, quickly nicknamed "mad cow disease," was clearly infectious, but the particular pathogen was difficult to identify. By 1993, 120,000 cattle in Britain were identified as being infected. As yet, no human cases had occurred and the UK government insisted that cattle were a dead-end host for the pathogen. By the mid-1990s, however, multiple human cases, attributable to ingestion of meat and organs from infected cattle, were discovered. In humans, variant Creutzfeldt-Jakob disease (CJD) was a media sensation — a nearly uniformly fatal, untreatable condition with a rapid onset of dementia, mobility issues characterized by jerky movements, and autopsy reports finding that the brain itself had turned into a spongy mess.

The United States banned UK beef imports in 1996 and only lifted the ban in 2020.

The disease was made all the more mysterious because the pathogen involved was not a bacterium, parasite, or virus, but a protein — or a proteinaceous infectious particle, shortened to "prion."

Prions are misfolded proteins that aggregate in cells — in this case, in nerve cells. But what makes prions different from other misfolded proteins is that the misfolded protein catalyzes the conversion of its non-misfolded counterpart into the misfolded configuration.